The present invention relates to vinylidene chloride polymer films, and more particularly to such films having reduced cooked-protein adhesion after exposure to retort or cook-in conditions.
Vinylidene chloride polymers (xe2x80x9cPVdCxe2x80x9d), such as vinylidene chloride/vinyl chloride copolymer (xe2x80x9cVDC/VCxe2x80x9d), display very low permeability to gases and vapors. For example, VDC/VC is a popular material to provide barrier attributes to monolayer and multilayer films. One example of the use of a monolayer film that contains VDC/VC is in retort packaging of a food product known as xe2x80x9cChinese sausage.xe2x80x9d
Chinese sausage is made by forming a flowable food emulsion containing a protein source (e.g., pork, chicken, beef, or seafood such as fish), a starch source, flavorings, and water. Separately, a biaxially-oriented monolayer VDC/VC film is formed into a tube by making a fin seal in the machine (longitudinal) direction, using a radio frequency sealing method. The bottom end of the tube is gathered and clipped closed by a metal clip. Then the food emulsion is pumped through the open top end of the tube to fill the tube. Next, the top end of the tube is gathered and metal-clipped closed to form a packaged food emulsion.
The packaged food emulsion is then exposed to conditions sufficient to cook (i.e., retort) the food emulsion. In China for example, the packaged food is heated from room temperature to from about 120xc2x0 C. to about 125xc2x0 C. over about a 20 minute period. The packaged food is then held at that temperature for about 20 minutes. Then, the packaged food is cooled down to room temperature over about another 20 minutes. In Korea, the total heating/maintaining/cooling cooking cycle is typically fasterxe2x80x94for example completed in about 40 to 45 minutes. During the exposure to the elevated temperatures, the packaging film shrinks about the packaged food to form a pleasing, tight appearance.
The Chinese sausage packaging film typically includes a narrow opening strip of plastic adhered to the outside of the package film along the length of the tube. To open the Chinese sausage, the consumer pulls the opening strip away from the filmxe2x80x94which tears the film and opens the package lengthwise. The consumer may then remove the ready-to-eat cooked sausage from the packaging.
If the cooked sausage adheres or sticks to the inside (i.e., food-side) of the packaging film, then small portions of the cooked sausage may break away from the bulk of the cooked sausage. This sticking or crumbling of the sausage visually displeases and annoys the consumer, causes a mess, and makes the consumer feel that he is wasting food product. Therefore, it is desirable to enable the consumer to easily remove the cooked sausage from the package without having the cooked sausage stick to the packaging film.
Although a PVdC film does not appreciably stick to pre-cooked Chinese sausage food emulsionxe2x80x94PVdC does tend to adhere to the packaged food once the PVdC and food emulsion have been placed in contact and exposed to the cooking conditions to form the cooked sausage. It is believed that one approach to decrease the meat adhesion of PVdC to the cooked sausage has been to incorporate a non-stick additive such as silicone or to increase the amount of plasticizer loaded into to the PVdCxe2x80x94that is, an amount of plasticizer above the minimum amount that is necessary to sufficiently enhance the processibility of PVdC so it can be biaxially oriented to a desired level. However, the non-stick additive and the additional plasticizer tends to decrease the barrier properties of PVdC and may also negatively affect the optical properties of the film.
The present invention addresses one or more of the aforementioned problems. A thermoplastic film has at least one external film layer that includes vinylidene chloride polymer. The external film layer also includes an amount of non-polar polymer effective to reduce the adherence to the external film layer of a cooked protein-containing food that is cooked while contacting the external film layer.
Another aspect of the invention is directed to a packaged food that includes a food and a package enclosing the food. The package includes a thermoplastic film having at least one external film layer that includes vinylidene chloride polymer. The external film layer also includes an amount of non-polar polymer effective to reduce the adherence to the external film layer of a cooked protein-containing food that is cooked while contacting the external film layer.
Still another aspect of the invention is directed to a method of providing a packaged, cooked food product. The method includes the step of forming a package having an least one opening. The package includes a thermoplastic film having at least one external film layer that includes vinylidene chloride polymer. The external film layer also includes an amount of non-polar polymer effective to reduce the adherence to the external film layer of a cooked protein-containing food that is cooked while contacting the external film layer. The external film layer forms a food-side layer of the package. Next, the open package is at least partially filled with a food product comprising at least about 20 weight % proteinaceous food. The package is closed. The closed package is exposed to conditions sufficient to cook the food product to a desired level.
Another aspect of the invention is directed to a method of reducing the cookedprotein adhesion attribute of a vinylidene chloride polymer-containing layer. First, from about 0.1 parts to about 5 weight parts of a non-polar polymer resin is mixed with 100 weight parts of a vinylidene chloride polymer resin. The mixture is formed into an external film layer.
The film and method of the present invention allow the use of a PVdC-containing layer as the food-side external layer of a retort or cook-in package, yet reduce the cooked-protein adhesion attributes of the layer in comparison to the same layer without the non-polar polymer. This allows the control of the amount of adhesion of the film to the cooked food product by varying the amount of non-polar polymer present in the PVdC-containing food-side external layer. In practice, the amount of non-polar polymer present may be increased to the extent that the cooked-protein adhesion of the layer is reduced to the point of non-adherence. Accordingly, when a protein-containing food (such as Chinese sausage emulsion) is packaged and retorted or cooked in a package made from the inventive film, then the consumer may open the package and remove the cooked food (e.g., cooked Chinese sausage) without the displeasing adherence of the food to the package film. Further, the reduced adherence attributes may be achieved without the need to load the PVdC layer with a non-stick additive such as silicone or a plasticizer above the amount needed merely to improve the processibility of the film.